Runtime 216 error on Citrix

Hi

I have SEP11 installed on several Citrix servers.  One of the servers is displaying this error when a user tries to access any item that uses Explorer in the Citrix environment:

Runtime 216 error at 77E678DF

Numerous web articles point the finger at the Subseven trojan, however the server's SEP11 client has detected nothing, and a full scan comes up clean.

Any suggestions - would there be any clues in the registry if this is a genuine infection?

Thanks